The present invention relates to a document reader for reading an image on a document surface of a document placed on a platen.
An image forming apparatus, such as a multifunctional printer, is provided with a document reader (see Japanese Patent Laid-Open Publication No. H07-193689 for example). Such a document reader employs at least one of a CIS (Contact-type image sensors) and a reduction-type image sensor.
Since the depth of field of the CIS is shallow, the document reader has to read the document surface while keeping substantially constant the image distance from the CIS to the document surface, in order to obtain a high-quality image. However, in copying a bound document for example, the image distance from the bound portion which is inevitably spaced upwardly apart from a platen glass falls out of the depth-of-field range, with the result that a blurred or distorted image is likely. This problem is essential not only to the Contact-type image sensors but also to the reduction-type image sensor, though there is a question of a degree.
Accordingly, the present invention intends to provide a document reader which is capable of ensuring a high-quality image even when the spacing between the document surface and the platen is uneven.